1. Field of the Invention
This invention relates generally to a mass storage disk drive and more particularly to the logic which controls the reading of the address portion of a sector of a track for verification, and then either writing or reading the data portion of the sector.
2. Description of the Prior Art
Mass storage disk devices includes a number of disks rotating about a common vertical axis. Both the top and bottom surfaces of each disk are typically coated with a magnetic material which retains magnetic bits. One read/write head is mounted on a carriage which moves in a radial and perpendicular manner to the common axis. Magnetic bits are written on the media surface when the carriage has positioned itself. Each head, therefore, would write in turn on the respective surfaces. The magnetic bit patterns for a surface are in concentric circles called tracks. The same track number on each surface represents a cylinder. The magnetic bit patterns are written in zones called sectors. Typically each track could be divided into 42 sectors. Therefore, to select a sector of data (magnetic bits), the disk device requires a cylinder number, a head number and a sector number. Data bytes are transferred between the disk device and a main memory, a sector at a time.
Each sector includes an address portion and a data portion. The address portion includes the cylinder number, the head number and the sector number.
After receiving the sector address, the disk drive positions the carriage to the cylinder and the addressed head reads the sectors, comparing the address sent to the disk drive with the addresses written in the address portion of the sector. When there is agreement, then the data portion of the sector is processed.
Related U.S. application Ser. No. 613,936 entitled "Single Revolution Disk Sector Formatter" describes the formatting of the address portion fields and the data portion fields of each sector of a track. Since the fields were written magnetically by the system to which the disk drive is operative, the sectors are called soft sectors. This is differentiated from the head sector disk where the sectors are laid out by the manufacturer.
Controllers for soft sector disks used a firmware/hardware technique for reading the address portion of a sector, then reading or writing the data portion. Such systems use a considerable amount of hardware and results in variable length gaps within the data portion of the sector due to variations in motor speed of the disk drive.